Morgan's work with fruit flies led to the discovery of X-linked genes. An older term "sex-linked genes" has been replaced with the more precise terms of X-linked genes and Y-linked genes.
Several linked genes on each type of chromosome are called a linkage group.
Crossing Over and Genetic Recombination
Linkage can be disrupted by crossing over. Crossing over is an exchange of parts of homologous chromosomes. The probability that crossing over will lead to the separation of two genes on a chromosome is proportional to the distance between them. This means that the farther apart two genes are, the greater their frequency of crossing over.
Crossing over introduces variations in genotypes and phenotypes and provides for the selection process necessary for evolution.
The animation describes (Audio - Important) on
crossing over.
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